Right, I've now been corrected by my girlfriend (biology graduate and
chronic asthma sufferer). Apparently all airways respond unfavourably
to cold air, but in the vast majority of cases it's not a problem. In
some cases it is a definite problem, but only when huge amounts of cold
air are being gulped down. This is usually termed "exercise-induced
asthma". Sufferers usually react especially badly either just after
starting or just after stopping an effort.
Symptoms include excess phlegm, wheezing, coughing or shortness of
breath. Shortness of breath is the one that causes a drop in athletic
performance, which is why riders from Indurain downwards have taken
medical remedies to stop even the slightest wheeze.
A quick Google for "exercise-induced asthma" shows, for example,
http://www.physsportsmed.com/issues/1999/11_99/lacroix.htm - which
looks like a seriously academic look at the problem.
"EIA develops when vigorous physical activity triggers airway narrowing
in people who have heightened bronchial reactivity (12). In short, EIA
is a reversible airway obstruction that occurs during or after
exertion; its symptoms include cough, wheezing, dyspnea[shortness of
breath], and/or chest tightness.
EIA can occur in otherwise healthy people who do not have chronic
asthma. Exercise is the only stimulus for their asthma symptoms."
Other information at
http://www.allergyasthma.com/archives/asthma16.html,
http://www.aaaai.org/patients/allergic_conditions/exercise_induced_asthma.stm
and numerous others.
Bottom line seems to be, if you have trouble with breathing in
excessively cold air, there are medical treatments (most commonly the
blue Salbutamol inhaler) which can help. However, asthma isn't
progressive (i.e. you're not gong to make matters worse) so there's
nothing particular to worry about. In fact given how impressive
"exercise-induced asthma" sounds relative to its actual impact, it's
probably worth hanging on to as an excellent excuse
cheers
marvin
now far better informed about asthma than he ever expected to be